This is a "performance painting" where I recited the number π from memory and by calculating an approximation with mental arithmetic.  

The shape of each cube was determined by my memory of π as I painted.  In total, I recited 5,584 digits from memory, with some inaccuracies (not marked).  The map between number and shape is based on the keyboard number pad, with 1 in the lower left and 9 represented by a complete square.  

At the same time I was reciting the repeating digits of the fraction 355/113 in the color of each cube.  355/113 is a close approximation of π.  

Since my memory of π is an approximation — as is the fraction — the painting is two approximations of π.  

The visual aesthetic of this painting was the result of careful preliminary studies and calculation.  The width of the painting is based on the number of digits before 355/113 "flips," with each 1 becoming an 8, each 2 becoming a 7, and so forth.  The repetition and predictable inversion forms the bands of color.  I explored many encoding mechanisms in advance, making this a key example in my work of data visualization.  

I followed up with: "Three Approximations of π," which was based on the simpler (and more famous) approximation of π, 21/7.  

I encoded the digits of π as cubes in a 3D model, then cut them in a series of aluminum bars in a CNC machine.  Finally, I recorded data from myself writing π several times, and used this as the basis for an intricate projection mapping onto the object.  

In this case, the "approximation" analogy arguably fails.